The 3.5A resolution structure of the membrane binding glyco-protein prothrombin fragment 1 will be extended to 2.8A resolution using multiple isomorphous replacement methods. Four excellent heavy atom derivatives are available along with one of lesser quality and a promising new candidate. The high resolution map will reveal the tertiary structure of the "kringle" sequence folded into a domain. The points of attachment of two disordered carbohydrate moieties will be determined from an "exact" difference map based on density modification using 2.8A resolution deglycosylated fragment 1 data. The two fragment 1 molecules crystallize isomorphously. Metal ion binding studies will be carried out with Mg+2 to induce the conformational change required for phospholipid-(PL)-fragment 1 binding. Similar studies with Ca+2, Sr+2 or Ba+2 will be used to determine and/or confirm Gamma-carboxy-Glu(G1a) residues in the folded structure which are involved in the PL binding and the nature of the Ca-Gla interaction will be delineated. The mother liquor of the crystals (tris maleate buffer, PEG) is benign toward all these ions. We will also initiate crystallization experiments aimed at growing a new crystal form of the structurally compact deglycosylated fragment 1 which should diffract x-rays beyond 2.8A resolution. We will approximate the structure of intact prothrombin and plasminogin by modelling of a serine protease and fragment 1 with one or more "kringle" folds on a PS 300 Interactive Graphics Display.